Packing boxes made of cardboard comprising a bottom portion including a rectangular bottom plane and three adjacent sides connected by a connecting strip to a lid portion including a rectangular top plane and three adjacent sides are well known. This type of box is used, in general, by bakers for boxing cakes or by clothing stores for boxing garments. Such boxes may have, on one side thereof, a locking mechanism including a flap associated with a closing element constituting both a handle and a latch for keeping the box closed. In order to use such a box it is necessary to manually close the lid and to subsequently extract the closing element which simultaneously provides both a handle and a locking system for the box. These packing boxes require sequential manual operations which cannot be made to be automatic in order to close and lock the box.
Other packing methods that allow for easy closure are known in the art. Such methods often require a tie, made of either string or ribbon, or some other means for surrounding the package to keep it closed. This tying operation can become burdensome and expensive for packaging a large series of objects.
Thus, a primary object of the present invention is to provide a packing box of simple construction which locks merely upon closing, requiring no tying or other manual manipulation to ensure locking. This object is achieved by providing at least one of the bottom sides of the above-described cardboard packing box having a pair of connected planes with adjacent sides with a flap and also providing a side of the lid portion with flap holding means for receiving the flap. The side of the lid portion opposite the bottom side provided with the flap is further provided with an opening for allowing fingers to pass through to unlock the flap when the box is folded to form a cubic volume. The flap and flap holding means of the present invention ensure that the box is automatically prevented from opening without outside intervention when the lid is snapped into placed over the bottom portion.